The invention relates to an electronic circuit comprising a first supply terminal and a second supply terminal and comprising a digital driver for driving a capacitive load, with an input terminal for receiving a digital input signal.
Such an electronic circuit is known from the prior art and is shown in FIG. 1. The electronic circuit has a first supply terminal VSS and a second supply terminal VDD for receiving a supply voltage which is delivered by a voltage source SV. The electronic circuit comprises a digital driver DRV1, a further digital driver DRV2, and a charge pump CHGP. The digital drivers are each constructed with an inverter known from the prior art in which one n-type field effect transistor and one p-type field effect transistor are used. The input of the driver DRV1 is coupled to the input terminal CLK for receiving a digital input signal UCLK. The output of the driver DRV1 is coupled to the input of the further driver DRV2 and to a first charge pump capacitor CP1. The output of the further driver DRV2 is coupled to a second charge pump capacitor CP2. In this manner the charge pump capacitors CP1 and CP2 are controlled in counterphase.
A disadvantage of the known electronic circuit is that the transistors T1 and T2 may both pass current simultaneously in the time period in which the digital input signal UCLK changes from a high value to a low value or from a low value to a high value, which will result in a short-circuit current between the first supply terminal VSS and the second supply terminal VDD. This makes the power consumption unnecessarily high.
It is an object of the invention to provide an electronic circuit with a digital driver which does not have the above disadvantage.
According to the invention, the electronic circuit mentioned in the opening paragraph is for this purpose characterized in that the digital driver comprises a first transistor with a first main current electrode which is coupled to the first supply terminal, a second main current electrode which is coupled for driving the capacitive load, and a control electrode; a second transistor with a first main current electrode which is coupled to the second supply terminal, a second main current electrode which is coupled to the second main current electrode of the first transistor, and a control electrode; a first capacitive element which is connected between the input terminal and the control electrode of the first transistor; and a second capacitive element which is connected between the input terminal and the control electrode of the second transistor.
The control electrodes of the first and the second transistor are thus connected to the input terminal not directly but via the first capacitive element and the second capacitive element, respectively. This renders it possible to adapt the voltages at the control electrodes of the first and the second transistor such that the first and the second transistor can never pass current simultaneously. A short-circuit current between the first and the second supply terminal is avoided thereby, so that the power consumption of the electronic circuit is reduced.
An embodiment of an electronic circuit according to the invention is characterized in that the electronic circuit further comprises means for providing a DC path between the control electrode of the first transistor and the first supply terminal, and for providing a DC path between the control electrode of the second transistor and the second supply terminal.
It is achieved thereby that the first or the second transistor is conductive during a short time period only. This is indeed the case immediately after a voltage level change in the digital input signal. During the remaining time, the potential of the control electrode of the first transistor is substantially equal to the potential of the first supply terminal, and the potential of the control electrode of the second transistor is substantially equal to the potential of the second supply terminal. Both the first and the second transistor do not pass current as a result of this.
Further advantageous embodiments of the invention are defined in claims 3, 4, and 5. An electronic circuit with a digital driver according to the invention may be used in various circuits in which a capacitive load is to be driven. The digital driver according to the invention may thus be used, for example, for driving charge pump capacitors of a charge pump.